Since the advent of a resist for KrF excimer laser (248 nm), an image forming method called chemical amplification is used as an image forming method for a resist so as to compensate for sensitivity reduction caused by light absorption. For example, the image forming method by positive chemical amplification is an image forming method of decomposing an acid generator in the exposed area upon exposure to excimer laser, electron beam, extreme-ultraviolet light or the like to produce an acid, converting an alkali-insoluble group into an alkali-soluble group by using the generated acid as a reaction catalyst in the baking after exposure (PEB: Post Exposure Bake), and removing the exposed area with an alkali developer.
As for the alkali developer used in the method above, various alkali developers have been proposed, but an aqueous alkali developer of 2.38 mass % TMAH (an aqueous tetramethylammonium hydroxide solution) is being used for general purposes.
Also, as an application of the above-described resist technology, a microfabrication application such as application to ion implantation employed when implanting an ion (charge injection), which is one step of the logic device fabrication or the like, is progressing.
In the case of using a resist composition for the application to ion implantation, the resist composition is sometimes coated, exposed and developed on a substrate previously subjected to patterning (hereinafter, referred to as a stepped substrate), and microfabrication on a stepped substrate is required. In the application to ion implantation, the task encountered in the patterning of microfabrication involving development with the above-described alkali developer and difficult to solve is the problem of scum on the substrate, which is generated after development due to bad release property of the film formed of the resist composition.
To meet a need from such a microfabrication technology, not only the currently predominant positive resist but also formation of a fine pattern by a negative image are being developed (see, for example, JP-A-2010-40849 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”), JP-A-2008-292975 and JP-A-2010-217884). Because, in the production of a semiconductor device or the like, patterns having various profiles such as line, trench and hole need to be formed and some patterns are difficult to form by the current positive resist.